1. The Field of the Invention
This invention relates to electrosurgery and, more particularly, to return electrodes adapted for providing effective and safe electrosurgical energy return without conducting or dielectric gels or polymers, which may be reusable and/or disposable.
2. The Relevant Technology
As is known to those skilled in the art, modern surgical techniques typically employ radio frequency (RF) power to cut tissue and coagulate bleeding encountered in performing surgical procedures. For historical perspective and details of such techniques, reference is made to U.S. Pat. No. 4,936,842, issued to D""Amelio et al., and entitled xe2x80x9cElectrosurgical Probe Apparatus,xe2x80x9d the disclosure of which is incorporated by this reference.
As is known to those skilled in the medical arts, electrosurgery is widely used and offers many advantages including the use of a single surgical tool for both cutting and coagulation. Every monopolar electrosurgical generator system, must have an active electrode that is applied by the surgeon to the patient at the surgical site to perform surgery and a return path from the patient back to the generator. The active electrode at the point of contact with the patient must be small in size to produce a high current density in order to produce a surgical effect of cutting or coagulating tissue. The return electrode, which carries the same current as the active electrode, must be large enough in effective surface area at the point of communication with the patient such that a low density current flows from the patient to the return electrode. If a relatively high current density is produced at the return electrode, the temperature of the patient""s skin and tissue will rise in this area and can result in an undesirable patient burn.
In 1985, the Emergency Care Research Institute, a well-known medical testing agency, published the results of testing it had conducted on electrosurgical return electrode site burns, stating that the heating of body tissue to the threshold of necrosis occurs when the current density exceeds 100 milliamperes per square centimeter.
The Association for the Advancement of Medical Instrumentation (xe2x80x9cAAMIxe2x80x9d) has published standards that require that the maximum patient surface tissue temperature adjacent an electrosurgical return electrode shall not rise more than six degrees (6xc2x0) Celsius under stated test conditions.
Over the past twenty years, industry has developed products in response to the medical need for a safer return electrode in two major ways. First, they went from a small, about 12xc3x977 inches, flat stainless steel plate coated with a conductive gel placed under the patient""s buttocks, thigh, shoulders, or any location where gravity can ensure adequate contact area to a flexible electrode. These flexible electrodes, which are generally about the same size as the stainless steel plates, are coated with a conductive or dielectric polymer and have an adhesive border on them so they will remain attached to the patient without the aid of gravity, and are disposed of after use. By the early 1980""s, most hospitals in the United States had switched over to using this type of return electrode. These return electrodes are an improvement over the old steel plates and resulted in fewer patient return electrode burns but have resulted in additional surgical costs in the United States of several tens of millions of dollars each year. Even with this improvement, hospitals were still experiencing some patient burns caused by electrodes that would accidentally fall off or partially separate from the patient during surgery.
Subsequently, there was proposed a further improvement, an Electrode Contact Quality Monitoring System that would monitor the contact area of the electrode that is in contact with the patient and turn off the electrosurgical generator whenever there was insufficient contact area. Such circuits are shown, for example, in U.S. Pat. No. 4,231,372, issued to Newton, and entitled xe2x80x9cSafety Monitoring Circuit for Electrosurgical Unit,xe2x80x9d the disclosure of which is incorporated by this reference. This system has resulted in an additional reduction in patient return electrode burns, but requires a special disposable electrode and an added circuit in the generator that drives the cost per procedure even higher. Fifteen years after this system was first introduced, fewer than 40 percent of all the surgical operations performed in the United States use this system because of its high costs.
The present invention overcomes the problems of the prior art by providing a return electrode that eliminates patient bums without the need for expensive disposable electrodes and monitoring circuits in specialized RF generators.
Briefly, the improved return electrode according to the preferred embodiment of the invention hereof includes an effective surface area that is larger than other return electrodes that have been disclosed or used in surgery previously. It is so large and so adapted for positioning relative to the body of a patient that it eliminates the need for conductive or dielectric gels. Moreover, the exposed surface is of a material that is readily washable and/or sterilizable so as to facilitate easy and rapid conditioning for repeated reuse. It employs geometries and materials whose impedance characteristics, at typically used electrosurgical frequencies, are such that it self-limits the current densities (and corresponding temperature rises) to safe thresholds, should the effective area of the working surface of the electrode be reduced below otherwise desirable levels. Accordingly, the need for the foregoing expensive monitoring circuits in specialized RF generators is eliminated.
In accordance with a feature of the invention, an electrosurgical return electrode is made sufficiently large to present sufficiently low electrical impedance and low current densities at typical electrosurgery frequencies used in medical procedures to reduce the possibility of excessive temperature elevation in adjacent patient tissue (i.e., by maintaining temperature (xe2x80x9cTxe2x80x9d) rise below six degrees (6xc2x0) Celsius), thus avoiding tissue necrosis or other undesired patient trauma.
In accordance with yet another feature of the invention, the working surface of the electrode (the electrode surface that is in contact with or in close proximity to the patient) is made sufficiently large in area so that in normal use, current flow will not be reduced to a point where it impedes the surgeon""s ability to perform surgery at the surgical site.
In accordance with yet another feature of the invention, in one embodiment, the electrosurgical return electrode is a simple single-layer construction, thus minimizing cost.
In accordance with yet another feature of the invention, in one embodiment, controlled electrical conductivity is imparted to the single layer of material by the inclusion therein of electrically conductive materials such as conductive threads or carbon black, thus conditioning conductivity as a function of surface area to levels which limit passage of current therethrough to safe values.
In accordance with yet another feature of the invention, in another embodiment, a moisture impervious working surface is provided for positioning adjacent an adjoining surface of the body of a patient, thus facilitating cleansing and reuse of the electrosurgical electrode.
In accordance with yet another feature of the invention, the aforementioned moisture impervious working surface is made resistant to normally encountered cleaning, disinfecting, and sterilizing agents, thus further facilitating cleansing and reuse.
In accordance with yet another feature of the invention, in another embodiment, a sleeve is provided for cooperative use with the electrosurgical electrode, thus protecting the electrode from inadvertent damage that might occur, for example, from accidental contact of the active electrosurgical instrument with the electrode surface.
In accordance with yet another feature of the invention, the electrical impedance of the materials in and adjacent to the working surface of the electrode is sufficiently elevated so as to limit current density at the working surface to a level below the threshold of patient tissue trauma, thus providing a self-limiting characteristic to prevent patient trauma in the event of accidental reduction of the effective working surface of the electrode.
In accordance with yet another feature of the invention, in one embodiment, the electrosurgical electrode is form-fitted to the operating table on which the electrosurgical procedure is to be performed, thus facilitating realization of other features of the invention.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.